Decision likely to heat up an already intense presidential campaign for the May 23-24 elections - the first freely contested presidential race in Egypt's history.

An Egyptian court has ruled that that the mother of a popular ultraconservative Islamist viewed as one of the strongest contenders for president is not a U.S. citizen, likely clearing the way for him to run in May elections.

Wednesday's decision was met with cheers of "God is great!" by thousands of Hazem Abu Ismail's supporters who had camped outside the court house in Cairo for hours, waiting for the decision.

Abu Ismail is a 50-year-old lawyer-turned-preacher with a large following of enthusiastic supporters, particularly from the country's ultraconservative Salafi movement.

The decision is likely to heat up an already intense presidential campaign for the May 23-24 elections - the first freely contested presidential race in Egypt's history.

A law put in place after the fall of President Hosni Mubarak last year stipulates that a candidate may not have any other citizenship than Egyptian - and that the candidate's spouse and parents cannot have any other citizenship as well.

The country's electoral commission said last week that it had received documents confirming that Ismail's mother was an American citizen, effectively disqualifying him from the race. The announcement sparked widespread protests by his supporters.

The prospects of Abu Ismail's return threatens to divide the votes of Islamists who have nominated a number of candidates.

Among the other contenders are Khairat el-Shater of the Muslim Brotherhood, the country's largest political group, who represents a more mainstream face of the Islamist movement than does Abu Ismail.

Mubarak's ex-spy chief Omar Suleiman also joined the race in a surprise move on Friday, the last day of applications.

The Cairo Administrative Court ruled that the authorities must provide Abu Ismail with a document confirming that his mother has only Egyptian nationality.

Abu Ismail had challenged authorities to produce evidence backing their allegations. He had argued that if his mother held any citizenship other than Egyptian, authorities must have local records of her dual nationality. Lawyers said the papers presented by authorities were insufficient.

Many Egyptians who acquire another nationality fail to register with the government here and are hence not recognized by Egypt as dual nationals.

Abu Ismail had said that the case against him was a plot by authorities and foreign powers to disqualify him because of his increasing popularity.

The presidential elections commission is currently vetting documents of all applicants for the elections and is to announce a final list before the end of the month.

Other candidates are also facing legal challenges, including the Brotherhood's el-Shater. Plaintiffs have challenged el-Shater's candidacy on grounds he had served time in prison connected to his political activity under Mubarak. He received a pardon from military rulers but his challengers say more time must pass before he can run, according to the law.

Suleiman, the ex-spy chief, is facing a challenge from the Islamist-dominated parliament. Parliamentary committees have been discussing passing a law barring former Mubarak officials from running for office.

Suleiman's bid for presidency has angered Islamists and revolutionary groups who say it was an offense to the 2011 uprising that toppled Mubarak.